Component alignment is of critical importance in semiconductor and/or MEMS (micro electromechanical systems) based optical system manufacturing. The basic nature of light requires that light generating, transmitting, and modifying components must be positioned accurately with respect to one another, especially in the context of free-space-optical systems, in order to function properly and effectively in electro-optical or all optical systems. Scales characteristic of semiconductor and MEMS can necessitate sub-micron alignment accuracy.
Consider the specific example of coupling a semiconductor diode laser, such as a pump laser, to a fiber core of a single mode fiber. Only the power that is coupled into the fiber core is usable to optically pump a subsequent gain fiber, such as a rare-earth doped fiber or regular fiber, in a Raman pumping scheme. The coupling efficiency is highly dependent on accurate alignment between the laser output facet and the core; inaccurate alignment can result in partial or complete loss of signal transmission through the optical system.
Moreover, such optical systems require mechanically robust mounting and alignment configurations. During manufacturing, the systems are exposed to wide temperature ranges and purchaser specifications can explicitly require temperature cycle testing. After delivery, the systems can be further exposed to long-term temperature cycling and mechanical shock.
Solder joining and laser welding are two common mounting techniques. Solder attachment of optical elements can be accomplished by performing alignment with a molten solder joint between the element to be aligned and the platform or substrate to which it is being attached. The solder is then solidified to xe2x80x9clock-inxe2x80x9d the alignment. In some cases, an intentional offset is added to the alignment position prior to solder solidification to compensate for subsequent alignment shifts due to solidification shrinkage of the solder. In the case of laser welding, the fiber, for example, is held in a clip that is then aligned to the semiconductor laser and welded in place. The fiber may then also be further welded to the clip to yield alignment along other axes. Secondary welds are often employed to compensate for alignment shifts due to the weld itself, but as with solder systems, absolute compensation is not possible.
Further, there are two general classes of alignment strategies: active and passive. Typically in passive alignment of the optical components, registration or alignment features are fabricated directly on the components or component carriers as well as on the platform to which the components are to be mounted. The components are then mounted and bonded directly to the platform using the alignment features. In active alignment, an optical signal is transmitted through the components and detected. The alignment is performed based on the transmission characteristics to enable the highest possible performance level for the system.
The basic problem with conventional mounting and alignment techniques is that they are incompatible with high-speed production processes that are capable of yielding a consistently high-quality product. Passive alignment can be performed quickly, but there are typically problems associated with producing high performance products. In contrast, active alignment production processes can be well optimized over time to yield the high performance devices. These processes, however, are typically very slow. For example, in laser welding, the optical fiber bracket must be first welded. The weld must be allowed to cool and then alignment subsequently checked. Subsequent welding may then be necessary, followed by further cooling and rechecking cycles.
Moreover, these conventional techniques are difficult to deploy in the manufacture of more-complex optical systems that offer higher levels of functionality. For example, laser welding has been successfully used to align the end of an optical fiber to a single laser diode chip in a small, i.e., less than five-centimeter module. It would be desirable, however, to integrate more functionality, such as filtering, multiplexing, demultiplexing, and/or switching capabilities in modules of similar dimensions.
The present invention concerns mounting and alignment structures for optical components, especially micro optic components having a size of typically less than a millimeter. The structures are preferably deployed in all-optical, electro-optical, electromechanical-optical devices/subsystems/systems. These structures are used to connect the optical components to an optical circuit board or optical bench. The optical components include active devices, such as lasers or other devices offering higher levels of functionality, such as integrated lasers/MEMS, e.g., tunable Fabry-Perot active devices. Still further, the optical components in other implementations are passive devices such as beam splitters, passive, such as thin film, filters, mirrors, birefringent material, polarizers, crystals, prisms, and/or diffractive elements, for example. More specifically, the invention is directed to a generalized mounting system that allows optical components to be connected to an optical bench and then subsequently aligned, i.e., either passively or actively, in manufacturing or subsequent calibration or recalibration, alignment or realignment processes.
In general, according to one aspect, the invention features a mounting and alignment structure for optical components. The structures typically comprise a quasi-extrusion portion. This portion is xe2x80x9cquasi-extrusionxe2x80x9d in the sense that it has a substantially constant cross section in a z-axis direction as would be yielded in an extrusion manufacturing process.
The invention, however, is not limited to only forming the structures via extrusion. For example, in the preferred embodiment, the structures are manufactured using a photolithography and metalization, such as metal electroplating, processes.
According to the invention, the quasi-extrusion portion comprises at least one base, having a laterally-extending base surface, and an optical component interface. At least one armature connects the optical component interface with the base.
In the preferred embodiment, the base surface is securable to an optical bench. In the preferred embodiment, the base surface is bonded to the optical bench via solder bolding, such as solder bonding with an 80/20 gold/tin ratio, or other eutectic solder. In alternative embodiments, however, laser welding, epoxy bonding, ultra-sonic welding, or adhesive/cast bonding are used.
In one embodiment, the base surface further comprises alignment features that are adapted to mate with opposite-gender alignment features of an optical bench. This passive alignment technique is used to facilitate initial positioning of the alignment structure on the optical bench. In the preferred embodiment, optically detectable alignment features or marks are used to position the structures on the bench.
Depending on the implementation, one or two bases are provided. In two base configurations, one is typically located on either side of a medial axis of the structure.
In the preferred embodiment, the interface comprises a port for enabling an optical signal to pass transversely through the quasi-extrusion portion. This enables optical access to an optical component installed on the optical component interface. In some implementations, an optical signal is reflected off of the optical component to pass back through the port. In other implementations, the optical signal passes through the optical component, in the case of a lens, for example.
In other implementations, the interface is configured as an open clamp or U-shaped cut-out. This configuration is useful for mounting optical components such as optical fibers to a bench.
Also preferably, the handle is provided to facilitate grasping and manipulation of the alignment structure. In one implementation, the handle is integral with the optical component interface. In other embodiments, handles are provided integral with the armature(s) and/or integral with the base(s).
In the preferred embodiments, the armature comprises at least one flexure. The flexure is typically a region of the armature that has a reduced cross-sectional area. Preferably, at least two flexures are provided along the armature. The flexures are preferably separated by a laterally-extending segment of the armature. Other flexures of the structure are preferably separated by vertically-extending segments.
Providing laterally and vertically extending segments allows for the manipulation and consequently alignment of the optical component on the structure in a two-dimensional x-y plane with a minimal of linkage between alignments along the x-axis with alignment along the y-axis.
The use of discrete flexures, however, is not a requirement. In other embodiments, the flexure is distributed in the fashion of a leaf spring across a region of the armature and in fact, the armature itself can act or function as a distributed flexure.
In general, according to another aspect, the invention also features a mounting and alignment structure for an optical component having a substantially-constant cross section in an x-y axis plane. The rigidity of the structure to strain in the x-y plane is greater than in the direction of a z-axis. The structure comprises at least one base having a laterally extending base surface and an optical component interface.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.